Final answer:
Blood gas instruments measure the sO₂ by using a pulse oximeter, which operates on the principle that hemoglobin absorbs various wavelengths of light in proportion to its oxygen saturation. Readings typically range from 95-100 percent, and lower levels indicate hypoxemia.
Step-by-step explanation:
Blood gas instruments measure the percentage of sO₂ (oxygen saturation) by using a device known as a pulse oximeter. This device is typically clipped onto a thin part of the body, such as the fingertip, and utilizes two different wavelengths of light (red and infrared). As these wavelengths pass through the finger, differences in light absorption by hemoglobin, based on its oxygen saturation, are detected by a photodetector. The oximeter calculates the percent saturation by comparing the light received with the amount absorbed by the hemoglobin. Normal pulse oximeter readings are typically between 95-100 percent; lower values indicate hypoxemia, which is a lower than normal level of oxygen in the blood.